The present invention relates to a heat-sensitive recording sheet for heat-sensitive recording using a thermal head.
Various non-impact type recording devices have been recently proposed. The demand for heat-sensitive recording devices as output devices for equipment such as information processors has increased since labor for maintenance or the like can be reduced to a minimum, no noise or other pollution is generated, and the construction of a heat-sensitive recording device is easy. For example, in a ticketing machine, this type of heat-sensitive recording device is used as a printing means for the tickets. However, since it is necessary to prevent alteration of tickets after issuing them and to secure the durability of the printing (especially in the case of a commutation ticket) for withstanding use over an extended period of time, a method has been desired which is capable of fixing the image after the heat-sensitive recording.
The thermally developing diazo-compound method is one example of a recording method which is capable of photofixing the recorded image. This method, however, is defective in durability. Among the thermally developing diazo-compound methods, the method which uses a recording material including a diazosulfonate offers the best advantages for heat-sensitive recording and photofixing due to the relative stability of the recording material in a dark environment.
Many studies have been made about the reaction of diasosulfonates to heat and light, and their optical behavior may be shown as follows: ##STR1##
As a recording method utilizing these characteristics, techniques are disclosed in the U.S. Pat. No. 2,217,189 for decomposing the diazosulfonate in the exposed part by the reaction (1).fwdarw.(2).fwdarw.(4) for pattern exposure or obtaining an image by the reaction (1).fwdarw.(2).fwdarw.(3) for color formation of the unexposed part by heating. Further, in the Japanese patent publication No. 51-43926, a method for producing the reaction (1).fwdarw.(2).fwdarw.(3) by simultaneously supplying light and heat is disclosed.
However, since a thermal head is generally used in heat-sensitive recording, and since there is a limit to the heat energy represented by the product of the temperature and time due to the service life of the thermal head, the above-mentioned methods cannot be utilized. In the method disclosed in the U.S. Pat. No. 2,217,189, the heat-sensitivity is low and the image density is low. In the method disclosed in the Japanese patent publication No. 51-43926, the fixing reaction (1).fwdarw.(2).fwdarw.(4) requires a large amount of exposure light and thus cannot be realized in ticketing machines.